Department of Chemistry, Washington University School of Medicine, St. Louis, Missouri, USA.

Abstract

Neuropathic pain is a debilitating condition for which the development of effective treatments has been limited by an incomplete understanding of its chemical basis. We show by using untargeted metabolomics that sphingomyelin-ceramide metabolism is altered in the dorsal horn of rats with neuropathic pain and that the upregulated, endogenous metabolite N,N-dimethylsphingosine induces mechanical hypersensitivity in vivo. These results demonstrate the utility of metabolomics to implicate unexplored biochemical pathways in disease.

N,N-dimethylsphingosine (DMS) elicits neuropathic pain behavior and cytokine release. (a) Immunohistochemistry of the dorsal horn of rats intrathecally administered DMS at 0.25 μg/Kg (left) and vehicle (right) and stained with anti-glial fibrillary acidic protein (anti-GFAP) and a Alexa fluor 488 anti-rabbit IgG secondary antibody (green). Increased GFAP staining, a marker of astrocyte activation, is seen in the dorsal horn of DMS-treated rats relative to vehicle controls. (b) ELISAs of IL-1β and MCP-1 released into the supernatant of astrocyte cultures treated with DMS or vehicle. Cultures treated with 0.1 μM of DMS show a significant increase in IL-1β and MCP-1 release relative to vehicle controls. Data are expressed as mean ± SEM, with n=3 cultures per group. (c) Comparison of S1P levels in the dorsal horn of rats intrathecally administered DMS at 1.6 μg/Kg and vehicle control. S1P was measured by selective reaction monitoring triple quadrupole mass spectrometry (QqQ). S1P levels between the groups are not statistically different (n=4 animals per group). S1P levels are represented as fmol per mg of spinal cord tissue. (d) Comparison of S1P levels in the ipsilateral dorsal horn of sham control animals relative to animals suffering from TNT 21 days after injury. S1P levels between the groups are not statistically different (n=7 animals per group). S1P levels are represented as fmol per mg of spinal cord tissue.